Klyflaccisteroids K-M, bioactive steroidal derivatives from a soft coral Klyxum flaccidum

New steroids, klyflaccisteroids K-M (1-3), were isolated from a soft coral Klyxum flaccidum. Their structures were elucidated on the basis of extensive spectroscopic analysis. Klyflaccisteroid K (1) is the unique 9,11-secosteroid with a 5,8-epidioxy-9-ene functional group. Klyflaccisteroid L (2) has an unusual 11-norsteroid skeleton and is the first example of 11-oxasteroid isolated from natural sources. Cytotoxicity assay showed that 1 and 3 possessed moderate to weak cytotoxicity against these cancer cells. Compound 1 was also found to display significant anti-inflammatory activity of suppressing superoxide anion generation (O₂^-) and elastase release, and compound 3 was found to show notable anti-inflammatory activity toward inhibition of elasstase release, too.